Abstract: In this paper,the author puts forward the theory for internal kidney and external kidney.The former is responsible for controlling water and corresponds with the urinary system in anatomy of western medicine;the latter is responsible for controlling essence and corresponds with the thalamus-pitutary-gonad axis system in anatomy and the external genitalia of western medicine.The two combined constitute the kidney in the sense of traditional Chinese medicine,which include the urogenital system,the thalamus-pitutary-gonad axis system(thyroid gland,thalamus,adrenal gland and gonad) and the neuroendocrine-immune network.The internal kidney and external kidney are anatomically connected and are related to and affect each other physiologically and pathologically.The internal kidney and external kidney are the keystone for the material and function of kidney in the sense of traditional Chinese medicine,and kidney yin and kidney yang are the application and embodiment of the material and function of kidney in the sense of traditional Chinese medicine.